JP3228252B2 - Radiation detector for radiation CT apparatus and radiation CT apparatus using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a radiation detector, and more particularly to a radiation detector used in a computed tomography (CT) apparatus using radiation such as X-rays and γ-rays.

[0002]

2. Description of the Related Art In a radiation CT apparatus, a large number of radiation detectors are arranged side by side at a position symmetrical to a radiation source (for example, an X-ray tube) with respect to an object to be photographed, and the radiation intensity at the position of each detector is measured. The internal structure of the object is observed. Since the radiation detectors arranged next to each other correspond to each pixel, the radiation detectors are made as small as possible and the interval between adjacent radiation detectors is reduced to increase the resolution and resolution.

The radiation detector has a structure in which a radiation scintillator and a semiconductor photodetector are stacked, and the scintillator is opened to the radiation source side to receive radiation such as X-rays by the scintillator. The scintillator is Cd
WO ₄ , Bi ₄ Ge ₃ O ₁₂ , Gd ₂ O ₂ S: Pr (C
e, F), etc., and emits visible light when radiation enters. The visible light is incident on a semiconductor photodetector attached to the back of the scintillator and is converted into an electric signal.
When radiation incident on a certain scintillator passes through the scintillator and re-enters an adjacent scintillator, the resolution is reduced. Therefore, a shielding plate is provided between the scintillators to prevent radiation from passing. Further, the visible light generated by the scintillator is generated in all solid angle directions, but needs to be guided to a semiconductor photodetector attached to the back of the scintillator. Therefore, the scintillator has a structure in which the periphery is covered with a light reflecting material except for a surface facing the semiconductor photodetector.

In order to attach a material having good light reflectivity to the surface of the scintillator, a metal such as aluminum is applied to a thickness of 0.1 to 5 μm by vapor deposition or sputtering. Aluminum is a metal with good light reflectivity, but the reflectance is about 80% even when aluminum is adhered to the scintillator surface, and the reflectance decreases to about 60% when an adhesive is applied between the scintillator surface and the aluminum plate. Resulting in. Therefore, as a light reflecting material, a white paint such as titanium oxide (TiO ₂ ), zinc white (ZnO), lead white (PbO), zinc sulfide (ZnS) is used so as to reflect visible light well.
Etc. are used. The light reflectance at a wavelength of about 500 nm is 94 to 96% for titanium oxide and 93 to 9 for zinc white.
It is about 4%, about 90 to 91% for lead white, and about 95% for zinc sulfide. Titanium oxide is often used as a light reflecting material because of its higher chemical stability against acids and alkalis than zinc white, lead white, and zinc sulfide. JP-A-59-183385 also discloses that an optical adhesive layer in which TiO ₂ powder is dispersed is used as a crosstalk preventing material.

[0005]

As described above, it is known that titanium oxide can be used as a light reflecting material of a radiation detector. However, as a light reflecting material, a light reflecting material having a higher light reflectivity is used. It is necessary to provide a material having a long life when exposed, that is, a material having good light resistance.

Accordingly, an object of the present invention is to provide a radiation detector using a light reflecting material having excellent light resistance.

It is another object of the present invention to provide a radiation detector using titanium oxide having a high light reflectance as a light reflecting material.

Another object of the present invention is to provide a radiation CT apparatus equipped with a radiation detector using a light reflecting material having excellent light resistance and good light reflectance.

[0009]

A radiation detector according to the present invention comprises a scintillator and a semiconductor light detecting element laminated on each other, and a light reflecting material is provided around the scintillator except for a surface facing the semiconductor light detecting element. Covered, the light reflecting material is made of a mixture of light reflecting material powder and resin,
The light reflecting material powder is made of rutile TiO ₂ .

In the present invention, it is preferable that at least one of Al ₂ O ₃ and SiO ₂ is attached to the surface of the rutile type TiO ₂ powder. The light reflecting material powder contains 85 to 99 wt% of TiO ₂ and Al ₂ O ₃
And it is preferable that at least one of SiO ₂ contains a 1 to 15 wt% in total. Further, the light reflecting material powder preferably has an average particle size of 0.15 to 1.0 μm.

[0011] A radiation CT apparatus according to the present invention is characterized by using the radiation detector.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A radiation detector according to the present invention and a radiation CT apparatus using the same will be described below in detail with reference to the drawings. Here, FIG. 1 is a perspective view of a radiation detector according to the present invention, FIG. 2 is a longitudinal sectional view of the radiation detector of FIG.
FIG. 3 is an enlarged perspective view of one of the radiation detectors of FIG. 1 taken out, FIG. 4 is a diagram illustrating a manufacturing process of the radiation detector of the present invention, and FIG. 5 is a diagram illustrating a radiation CT apparatus. 6 is an explanatory diagram of a test piece for measuring light reflectance.

A radiation detector according to the present invention is shown in FIGS.
As shown, a plurality of radiation detectors 2 are
Installed. Each radiation detector 2 is made of silicon, etc.
The scintillator 22 is mounted on the
A semiconductor light is provided around the scintillator 22.
Except for the surface facing the detecting element 21, the light reflecting material 23
Covered. The scintillator 22 is CdWO_Four, Bi_Four
Ge_ThreeO₁₂, Gd_TwoO _TwoS: Made with Pr (Ce, F) etc.
And the top surface, that is, with the semiconductor photodetector
Face opposite to the radiation source is facing the radiation source
Radiation enters the scintillator 22 from the surface
I do. The periphery of the scintillator 22 is covered with a light reflecting material 23.
The radiation incident on the scintillator 22
The generated visible light is guided to the semiconductor photodetector 21. Half
A current flows through the conductive light detecting element 21 due to the visible light received.
So that the electrodes of the semiconductor photodetector 21
Connecting the electrode 11 connected to the board to the radiation detection circuit
The radiation dose can be measured. Semiconductor photodetector 2
The configuration and function of 1 are already well-known, so the description is omitted.
I do.

As the light reflecting material 23, a material obtained by hardening a light reflecting material powder mainly containing rutile type titanium oxide (TiO ₂ ) with a thermosetting resin is used. Titanium oxide has anatase type, rutile type, and brookite type as its crystal structure. Anatase type and rutile type are preferred as white light reflecting materials, and among them, rutile type titanium oxide has excellent light resistance.

The mixing ratio by weight of the light reflecting material powder and the thermosetting resin (eg, epoxy resin) is preferably 0.5 or more for the thermosetting resin 1 and the light reflecting material powder. This ratio can be changed depending on the light reflectance to be obtained. However, by setting the light reflecting material powder to 0.5 or more relative to one thermosetting resin, the light reflectance (in this specification, there is no particular notice) As long as the light reflectance for monochromatic light having a wavelength of 512 nm) can be 90% or more. The upper limit of the mixing ratio is not particularly limited as long as it can be molded as a light reflecting material, but if the light reflecting material powder is 5 or 6 or more in comparison with the resin, molding becomes difficult. The preferred mixing ratio is in the range of 0.5 to 3.

The average particle size of the rutile type titanium oxide used is preferably 0.15 to 1.0 μm. Particle size is 0.
When the diameter is smaller than 15 μm, the light reflectance decreases, and
It becomes less than 0%. Similarly, when the particle size is larger than 1.0 μm, the light reflectance is similarly reduced to less than 90%. By using the rutile type titanium oxide light reflecting material powder having a particle size of 0.15 to 1.0 μm, the light reflectance becomes 90% or more.

The particle surface of the light reflecting material powder is made of Al ₂ O ₃ and S
It is preferable that at least one of iO ₂ is surface-treated. In particular, the composition of the light reflecting material is a TiO ₂ 85 to 99
When the total is 1 wt% to 15 wt% of at least one of Al ₂ O ₃ and SiO ₂ , the light reflectance becomes 90% or more. If the total of at least one of Al ₂ O ₃ and SiO ₂ is less than 1 wt% or more than 15 wt%, the light reflectance becomes less than 90%.

The radiation detector of the present invention can be manufactured by the manufacturing steps shown in FIG. First, the scintillator 22 is arranged on the adhesive sheet 42 as shown in FIG. Next, in (b), the mold 43 is placed on the adhesive sheet 42 so as to surround the scintillator 22, and the epoxy resin and the light reflecting material powder are mixed at a weight ratio of 1:
The mixture of 0.5 to 3 is poured into the mold 43,
The mixture is cast around the scintillator 22. This is heated for several hours at the temperature at which the epoxy resin cures in the air,
The resin solidifies. Next, the adhesive sheet 42 and the mold frame 43 are removed, and machining is performed to obtain a scintillator 22 as shown in FIG. The radiation detector is obtained by assembling with the semiconductor light detecting element 21 and attaching to the substrate 1.

As shown in FIG. 5, a radiation CT apparatus using a radiation detector has a subject 51 at the center of the CT apparatus 5.
Can be provided. Subject 51
A radiation source (for example, an X-ray tube) 52 is arranged so as to be able to move around the object, and the radiation detectors 2 are arranged side by side at a position facing the radiation source 52 with respect to the imaging target 51. The fan-shaped radiation 53 emitted from the radiation source 52 is absorbed by each part of the imaging target 51, and a shadow of the imaging target 51 is generated on the radiation detector 2. Thus, the contrast of the shadow of the object 51 can be obtained. The radiation source 52 and the radiation detector 2 are
, The same measurement is performed while rotating, and the measured values are combined and reconstructed into an image to obtain a CT image. By using a radiation detector having a light reflective material with high reflectivity as in the present invention, the output of the detector is increased, so that a radiation CT apparatus with extremely high sensitivity can be obtained. Further, even when the width of each radiation detector is narrowed by making the scintillator small, sufficient sensitivity is obtained because the output is large, and a CT device with high resolution can be obtained.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The light reflector used in the radiation detector of the present invention will be described in more detail by the following experiments.

Experiment 1 A light resistance test was performed on rutile-type titanium oxide and anatase-type titanium oxide. Rutile-type titanium oxide powder (average particle size of about 0.30 μm), the surface of which is coated with Al ₂ O ₃ and SiO ₂ at 1 wt% each, non-coated, and anatase-type titanium oxide powder (average particle size About 0.30μm
(1% by weight of each of Al ₂ O ₃ and SiO ₂ ) was mixed with an epoxy resin to obtain a light reflection material mixture of the titanium oxide powder 2 and the epoxy resin 1 in a weight ratio. As in a test piece 6 shown in FIG. 6, each of the light reflecting material mixtures 61 was applied to a Mo plate 62 having a thickness of 1 mm and a size of 20 mm × 30 mm. The coated surface of the Mo plate 62 is lap-finished so as to have a roughness Ra of about 4 seconds.
The light reflecting material 61 was uniformly applied thereon so as to have a thickness of 50 to 60 μm. By setting the light reflecting material 61 to such a thickness, light does not reach the Mo plate surface. Using this test piece 6, the reflectance at a wavelength of 512 nm was measured with a spectrophotometer.

For each test piece, the reflectance was measured immediately after the light reflecting material was applied and cured, and then the reflectance was measured while changing the period of exposure to natural light. Table 1 shows the exposure period and its reflectance. As is evident from the results, rutile-type titanium oxide has better light resistance than anatase-type titanium oxide. Rutile-type titanium oxide which has been surface-treated with Al ₂ O ₃ and SiO ₂ and has the best light resistance and light reflectance is the most suitable.

[0023]

[Table 1]

Experiment 2 A light reflecting material powder produced by applying a fine powder of Al ₂ O ₃ and SiO ₂ to the surface of a rutile type titanium oxide (average particle size of about 0.30 μm) powder was reduced to a weight ratio of 1. On the other hand, a light reflecting material mixture in which an epoxy resin was mixed at a weight ratio of 1 was applied to the Mo plate surface and cured to prepare a test piece as shown in FIG. Table 2 shows the results of measuring the reflectance of the test piece at a wavelength of 512 nm with a spectrophotometer. Table 2 shows the light reflectance and the output ratio with respect to the composition of the light reflecting material. The output ratio is Gd ₂ O using the Mo radiation shielding plate using each light reflecting material.
₂ Prepare a radiation detector adhered to S: Pr (Ce, F) scintillator, and output the X-ray at a tube voltage of 120 kV when irradiating X-rays, without rutile type titanium oxide surface treatment Is shown as a relative value with the output as 100. As is clear from Table 2, Al ₂ O ₃
And at least one of SiO ₂ is 1 to 15 wt% in total
Those included have a light reflectance of 90% or more and an output ratio of 110% or more.

[0025]

[Table 2]

Experiment 3 Rutile-type titanium oxide powder whose average particle size was changed from 0.10 μm to 2.0 μm was subjected to a coating treatment of Al ₂ O ₃ and SiO ₂ in a total of 2 wt% on each surface. Light reflecting material powder is used, and the light reflecting material powder is 1 in weight ratio.
A test piece as shown in FIG. 6 was prepared using a light reflecting material mixture obtained by mixing the epoxy resin 1 with the light reflecting material. The light reflectance was measured with a spectrophotometer at a wavelength of 512 nm, and the output ratio of the radiation detector was measured in the same manner as in Experiment 2.
BR> shown in Table 3. As is clear from Table 3, the average particle size of the rutile type titanium oxide powder is 0.15 to 1.0 μm.
In this case, the light reflectance is 90% or more, and the output ratio is 110%.
% Or more.

[0027]

[Table 3]

[0028]

As described above, since the radiation detector of the present invention uses a light reflecting material having a light reflectance of 90% or more and excellent light resistance, the radiation detector has an output of 110% or more as compared with the conventional one. , With good detection sensitivity. A radiation CT apparatus using this radiation detector can have a high resolution.

[Brief description of the drawings]

FIG. 1 is a perspective view of a radiation detector according to the present invention.

FIG. 2 is a longitudinal sectional view of the radiation detector of FIG.

FIG. 3 is an enlarged perspective view of one of the radiation detectors of FIG. 1 taken out.

FIG. 4 is a diagram illustrating a manufacturing process of the radiation detector of the present invention.

FIG. 5 is an explanatory diagram of a radiation CT apparatus.

FIG. 6 is a perspective view of a test piece for measuring light reflectance.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 11 Electrode 2 Radiation detector 21 Semiconductor photodetector 22 Scintillator 23 Light reflection material 42 Adhesive sheet 43 Formwork 5 Radiation CT apparatus 51 Object to be photographed 52 Radiation source 53 Radiation 6 Test piece 61 Light reflection material mixture 62 Mo plate

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takeo Sasaki 2-1-2 Marunouchi, Chiyoda-ku, Tokyo Inside Hitachi Metals Co., Ltd. (56) References JP-A-62-47568 (JP, A) JP-A-9 -21899 (JP, A) JP-A-1-202684 (JP, A) JP-A-3-238387 (JP, A) JP-A-2-266287 (JP, A) JP-A-5-45468 (JP, A) JP, 5-19060 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01T 1/20

Claims (3)

(57) [Claims] 1. A laminated scintillator and a semiconductor photodetector
Arranged side by side a plurality of child, in the radiation CT apparatus for a radiation detector the surrounding scintillator except a surface facing the semiconductor photodetector of that <br/> covered with light reflecting material, the light-reflecting material consists of a mixture of a light-reflecting material powder and a resin, said light reflective material powder of rutile type TiO ₂ 8
5～99Wt% and, Al ₂ O ₃ and the radiation CT apparatus for a radiation detector, characterized in that at least one of SiO ₂ contains a 1 to 15 wt% in total. 2. The light reflecting material powder has an average particle size of 0.1.
The radiation detector according to claim 1, wherein the radiation detector has a thickness of 15 to 1.0 m. 3. A radiation CT apparatus using the radiation detector according to claim 1.